A device and a module according to the invention are adapted in particular to supply satellites with electrical energy generated by a solar generator.
The electrical power supply network of a satellite generally includes a main power supply bus to which are connected a solar generator that consists of a plurality of individual generators, an electrical energy storage device that includes one or more batteries, and the equipment to be supplied with power. The solar generator must at the same time supply power to the main bus and charge the energy storage device, which device takes over from the generator during periods of eclipse and assists it to manage peaks in consumption of energy by the equipment. Moreover, it is also necessary to provide a mechanism for dissipating excess energy that may be produced by the solar generator, in particular under conditions of strong illumination and low consumption by the equipment.
The voltage of the main bus is conventionally regulated by selectively connecting the individual solar generators to said main bus or by short-circuiting them. If the voltage level on the main bus tends to increase, one of the individual generators assigned to supplying it with power is short-circuited; conversely, if the voltage level on the bus tends to decrease, one of the short-circuited generators is connected to it. A dedicated device controls charging of the batteries via the main bus and discharging of the batteries if the energy produced by all the solar generators proves to be insufficient to maintain a nominal voltage level on said main bus. This principle, known as an S3R (sequential switching shunt regulator) architecture, is described in the document BE 853124 and in the paper by D. O'Sullivan and A. Weinberg entitled “The Sequential Switching Shunt Regulator S3R”, Proceedings of the Third ESTEC Spacecraft Power Conditioning Seminar, 21-23 Sep. 1977 (ESA SP 126, pages 123-131).
The document FR 2 785 103 discloses a significant improvement to the S3R architecture in which a three-state control device selectively connects each solar generator to a power supply bus or to an electrical energy storage device, or short-circuits it. In this way, the three-state control device regulates the voltage on the main bus and at the same time charges the batteries, eliminating the requirement for a separate charging regulator. The resulting significant simplification makes the power supply system more reliable and increases its energy efficiency. This improved architecture is known in the technical literature as the S4R (sequential and serial switching shunt regulator) architecture.
The document FR 2 828 962 describes a complete voltage regulation system for a main power supply bus including a plurality of S4R modules.
FIG. 1 shows one example of an S4R control device including a control unit L that controls two switches I1 and I2 as a function of a first signal NTBA indicating the voltage level of said power supply bus and a second signal NTCB indicating a battery charging voltage level. A simple inspection of the circuit shows that the generator G supplies the main bus BUS with electrical energy when the two switches are open, charges the battery BATT when the switch I2 is open and the switch I1 is closed, and is short-circuited if the switch I2 is closed, regardless of the state of the switch I1.
A drawback of the FIG. 1 control device is that failure of the control unit L, of the means for generating the second signal NTCB, or of the switch I1 can cause the said switch to stick in the closed position, which is liable to overcharge the batteries and therefore damage them. This problem is particularly acute if the maximum battery charging voltage is lower than the nominal voltage of the main bus.
This problem is highlighted by the document FR 2 785 103 itself, which proposes to solve it by forcing closure of the switch I2 if the switch I1 is closed when the second signal NTCB indicates a relatively high level of charge of the batteries, which should have caused it to open.
This solution is not entirely satisfactory, as it is effective only against a failure occurring at the level of the switch I1 itself, and is without effect in the event of a malfunction of the control unit L. In fact, in the event of failure of the control unit, it would not be possible to force the closure of I2 and therefore to implement the protection. Similarly, failure in the means for generating the second signal NTCB could render the proposed protection mechanism inoperative.
It follows that an isolated fault (i.e. one concerning only one element) occurring in only one of the numerous control devices included in a complete voltage regulation system for a main power supply bus is liable to lead to irreparable deterioration of an essential component of said system, namely the electrical energy storage device.
The document FR 2 828 962 does not propose any solution to this problem. To the contrary, it gives detailed electrical schematics of S4R modules that do not even implement the partial protection mechanism of the document FR 2 785 103.